The present invention relates generally to automatic heating appliances, and more particular to a microwave oven having means for automatically determining an appropriate heating condition of an object to be heated for cooking purposes on the basis of a distinctive feature of the object.
One known heating appliance for heating an object, i.e., food, for cooking purposes is a microwave oven having various sensors whereby the heating of the object is automatically and appropriately effected on the basis of the sensed information such as temperature and humidity. The density of the object is also important cooking information necessary in order to perform the cooking in accordance with the class of the object to be heated. To obtain the object density, it may be necessary to know the weight and the volume or configuration of the object. One known way of obtaining information regarding the configuration of an object is disclosed, in Japanese Patent Provisional Publication No. 59-44793; automatic heating apparatus having a light source and an image pickup device arranged so that the configuration of an object to be heated is detected optically on the basis of an image produced on the image pickup device by a light ray from the light source. Important problems effecting such an optical type automatic heating appliance are dirt or stains deposited on the optical elements such as the lens with the passage of time and the generation of gases or vapors during heating which result in difficulty of an accurate recognization of the object configuration. Furthermore, this type of optical system may be limited in use to a particular type heating apparatus because of adverse effects caused by certain non-compatible heaters. Additionally, this type of optical system may involve high manufacturing costs because of the many parts required.